added the numpy_helper for einsum again in pbc branch
added the numpy_helper for einsum again in pbc branch

gkc1000/pyscf,gkc1000/pyscf,sunqm/pyscf,sunqm/pyscf,gkc1000/pyscf,sunqm/pyscf,sunqm/pyscf,gkc1000/pyscf,gkc1000/pyscf